The petroleum industry has long struggled with the problem of removing deposits of paraffin, asphaltines, and resins in oil producing formations, and in surface production systems such as pipelines and storage tanks. Prior art techniques for removing these deposits include various chemicals and mechanical cleaning techniques.
Organic deposits are initially in solution within the crude oil which is produced from the reservoir. This oil is pumped from the well and up a tubing string, out through the wellhead and to the separation facilities to oil storage facilities. During the production and transport of the crude oils, the equilibrium of the solution is altered, and paraffin waxes, resins, and other organic materials become less soluble and precipitate out of the solution, and are then deposited on the walls of the transport systems. These deposits accumulate sufficiently to restrict the oil flow, thereby resulting in lower oil production and thus reduced net profits. To improve the production flow rate, the deposits must be periodically removed.
Prior art methods to remove such deposits involve the use of xylene, toluene, and other aromatic based solvents, which may be mixed with selected dispersants to solubilize the deposits. Special chemical blends have been proposed that generate heat as a result of an exothermic reaction, but these blends often require a substantial amount of surface preparation, mixing time, or downhole circulation time. Accordingly, techniques which use selected chemicals to produce an exothermic reaction and thereby remove deposits from wells and pipelines have not been favored for many applications.
U.S. Pat. No. 3,279,541 discloses a method of removing paraffins and asphaltines from a well. An inorganic salt or base which evolves a large amount of heat upon the addition of water is preferred as the heat generating solution. Disclosed materials include aluminum chloride, magnesium chloride, calcium chloride, sodium hydroxide, and potassium hydroxide. An inorganic salt such as calcium chloride may be added to water to cause a rise in the temperature of the water in the range of 200° F.
U.S. Pat. No. 6,756,021 discloses a device for the elimination of paraffin hydrate deposits in oilfield drilling equipment. An annular decomposition chamber may be mounted and sealed around a section of piping. The chamber contains a catalyst that promotes decomposition of the reactants.
U.S. Pat. No. 4,755,230 discloses another method of removing paraffin deposits from the interior of a hydrocarbon transmission conduit. An isolated length of the conduit receives an emulsified mixture of an aqueous solution and a hydrocarbon solution. In-situ nitrogen generating components and a buffered pH adjuster abate the reaction time to effect temperature melting of the paraffin deposits.
U.S. Pat. No. 4,775,498 discloses an oil and water emulsion with an organic solvent and agents selected to promote stable foamed emulsion.
U.S. Pat. No. 4,089,703 discloses a hot detergent process. One of the two solutions includes concentrated sulphuric acid and a foam stabilizer.
U.S. Pat. No. 6,176,243 discloses a composition for paraffin removal. The composition includes an aliphatic alcohol and an organic acid selected from acetic acid, citric acid or formic acid.
The disadvantages of prior art compositions and techniques, and particularly those techniques designed to generate exothermic reactions to heat the downhole deposits, involve concerns with respect to the safety and the handling of the various composition chemicals at a well site or along a pipeline. Moreover, prior art exothermic techniques have not reliably produced a controlled reaction, and instead the actual reaction may produce more or less heat than desired. Producing more heat than desired can have severe adverse consequences on the walls of the equipment being cleaned, while a temperature reaction lower than desired is not likely to be effective at removing the paraffin deposits. In addition to the risks associated with utilizing prior art chemical compositions for this purpose, some of the compositions are very expensive and are thus not cost effective when used on numerous wells and pipelines. Other chemicals cause potential adverse consequences with the downhole equipment, such as corrosion. Still other compositions inherently involve lengthy processing and/or mixing times of the chemicals, which are not favored, particularly at the well site or the pipeline.
The disadvantages of the prior art are overcome by the present invention, which discloses a relatively simple and highly reliable composition for obtaining a controlled exothermic reaction to generate a desired amount of heat to remove paraffin, asphaltines and resins along a surface of a crude oil transmission system.